A driver of a tractor-trailer rig, also known as a semi, which has a trailer portion large enough to obstruct the view directly behind the tractor, must rely exclusively on outside rear view mirrors to see the area behind the trailer. When such tractor-trailers are traveling forward on a road or highway, hand adjustable outside rear view mirrors are generally satisfactory for providing the appropriate view of the rear corners of the trailer. On such vehicles, the driver simply adjusts both outside mirrors by hand when the trailer is straight. A standard exterior side-view mirror normally provides only a limited field of view.
However, when the driver is maneuvering the tractor-trailer rig in close quarters, such as loading docks, and particularly when backing, the trailer is turned relative to the tractor so that the normal rear view from one of the fixed outside mirrors is usually partially or totally blocked by the bulk of the trailer. Further, the view from the other mirror is substantially divergent from the rear corner of the vehicle. This is known in the trucking industry as "blind side driving", and is a cause of many accidents costing millions of dollars annually.
One method of dealing with this situation is for the driver to make a series of small, incremental adjustments to the mirror for each few feet that the trailer is moved. With each move, the driver must get out of the tractor and walk beyond the trailer to check the progress, and adjust the mirrors accordingly. These steps are repeated many times until the trailer is satisfactorily parked or otherwise positioned. While this method is often instructed by trucking companies, and is considered mandatory by the U.S. Department of Transportation, it is seldom used by drivers for reasons of convenience and excessive time consumption. Instead, the "best guess" method is often used. To do this, the driver simply uses the extremely limited visual information available from the driver's seat and guesses the location of the trailer relative to the rest of the environment. This often results in many unnecessary accidents.
Previous attempts to solve these problems have been made by redesigning the mirrors themselves to include the use of wide angle or "fish-eye" lenses and the use of remote controlled rear view mirrors. With the former, the use of wide angle lenses results in substantial distortion of the driver's view, including loss of depth perception and detail. This makes the image available from such mirrors unreliable for close quarter or precise maneuvering.
One example of a remote-controlled mirror includes a four-way control provided so that the driver can manually adjust both of the mirrors in the horizontal and vertical axes from the driver seat. Such systems are generally not satisfactory since the driver is simply too busy to constantly adjust the mirror controls to compensate for the turning trailer while simultaneously guiding the tractor-trailer in its rearward course. Further, the driver is not always assured of the proper viewing angle while turning the tractor trailer.
One attempt to create an automatic mirror tracking control system is found in U.S. Pat. No. 5,132,851 to Bomar. This system utilizes a steering wheel linkage as a pick-up wheel to determine relative vehicle angles; an ultrasonic transducer; and a radio frequency control link to the servo motor effecting mirror movement. This system has certain drawbacks making the automatic tracking of the side view mirror problematical. First, a very complicated steering wheel linkage system is used which does not correctly reflect relative vehicle angles in a backing situation. For example, if a trailer is at some non-zero angle when the tractor starts to back up, the trailer will increase in turning angle relative to the tractor without the steering wheel being turned so that the increase in angle is not recognized by the system. Consequently, the steering wheel linkage would provide no information to the driver under such conditions. The calibration of the linkage to every type of tractor-trailer arrangement is an awkward and time-consuming task, mitigating against use of this system for a wide variety of tractor-trailer combinations.
The second embodiment is described in the text from columns 6, line 13 through column 9, line 38, referring to FIGS. 9-12. This embodiment is described as essentially retaining the features of the first embodiment but utilizing at least two transducers mounted on the tractor or cab and a microchip in the control unit. The control unit includes rotatable dials (117 and 118 in FIG. 9) to set the distances in feet and inches from the fifth wheel of the tractor to the left side mirror. The same is done for the distance between the driver and the left side mirror. The distance from the driver to the right side mirror is preferably set in a memory of the microchip at the factory. Further programming of the control unit is done by using push button 135 (in FIG. 9) to set the length of the trailer (the distance from the fifth wheel on the tractor to the center of the rear axle). A transmitting antenna 138 is used to transmit control signals from the control unit to the mirror.
A key aspect of the control unit 114 is the microchip that controls the operation of the mirror tracking system. The vehicle dimensions are manually input by the operator (distance from the fifth wheel of the tractor to the left side mirror and distance from the driver of the tractor to the left side mirror) and are stored in the memory of the microchip. The length of the trailer is also stored after being input using manual push buttons. This information, as well as the current angle between the tractor and the trailer is used by the microchip to generate an electric signal which is transmitted via a transmitting antenna to a receiver unit, which in turn transfers control signals to the mirror motor.
The transducers (170 and 171 in FIG. 12) are mounted on the rear portion of the tractor. Preferably, there are two transducers mounted approximately 4 inches above a plane determined by the top of the fifth wheel of the tractor (as depicted in FIG. 12). By measuring the time taken for the emitted ultrasonic sound waves to be reflected back to the transducers, the distance between the respective and the trailer can be determined.
It is noted that the precise techniques used to calculate the angle based upon ultrasonic emissions and receptions from the two transducers is not disclosed. However, the technique can be surmised as one involving the data manually input in the system as part of the installation process. These include in particular, null zone information based upon steering wheel position; the distance from the fifth wheel of the tractor to the left side mirror; the distance from the driver to the left side mirror; the length of the trailer. All of this information is necessary for calculation of the angle between the tractor and the trailer.
The Bomar system is described as requiring only one ultrasonic transducer to measure the distance and turning angle. However, the result is not always accurate since the measured distance decreases to a minimum at some turning angle depending on the location of the transducer, and then increases until 80.degree. is reached. Consequently, when using a one transducer configuration, the direction of the turning trailer would not be known for a large portion of the turning radius centered around this minimum distance point since the data would start to repeat. The same result would occur even for two transducers spaced evenly apart from the center line of the vehicle. It is further noted that the radio-controlled mirror movement is not recognized by the system since there is no feedback mechanism indicating the exact position of the mirror. Consequently, some errors will always be introduced resulting in the driver not seeing the rear side corner of the trailer under some conditions.
The problems of mirror tracking for a backing tractor trailer are addressed by a similar system found in U.S. Pat. No. 4,679,158 to Tate. Like the Bomar system, the Tate system uses a steering wheel linkage, resulting in the same inaccuracies as described with respect to the Bomar system. This system also uses a stepping motor requiring a modulated pulse signal to move the mirror. This is activated by a radio frequency direction finding system with components mounted on both the trailer and the tractor. It is noted that accurate angle measurement between the tractor and the trailer becomes problematical for angles exceeding 60.degree. due to the inside of the edge of the trailer interfering with the RF path to the receiver. Also, the rotating mechanical linkage is located next to the "fifth wheel" where large amounts of grease and dirt accumulate, making a long-term accuracy of this component problematical.
It is noted that both of the aforementioned conventional examples of automatic side view mirror tracking systems share limitations regarding accuracy and long-term operability, as well as other problems caused by complex mechanical systems. It is clear then that a safe and reliable automatic rear view mirror tracking control system is needed for semitrailers and other articulated vehicles. Such a control system should constantly adjust mirror angles to compensate for varying tractor-trailer angles occurring as the trailer is turned relative to the tractor. Further, this system should not interfere with the driver's primary task, i.e., controlling the vehicle, and should be accurate at all possible positions between the tractor and the trailer, as well as compensating for various incongruities between steering wheel position and tractor-trailer position. Such a system should not be susceptible to breakdown caused by the environment in which an associated vehicle operates.
A superior approach is found in allowed U.S. Pat. No. 5,719,713 to Brown. Unlike the aforementioned examples of conventional systems, the Brown system does not rely upon mechanical linkages to the tractor trailer rig in order to calculate the angle between the tractor and trailer. Rather, this function is carried out entirely by three sets of ultrasonic transducer pairs located equidistantly across the rear portion of the top of the tractor. In each transducer pair, each transducer servers as both transmitter and receiver. Each transducer pair receives only the signals originally irradiated by itself. Thus, the number of possible measurements is limited. The angle of the tractor to the trailer is derived using look-up tables that correlate the times measured by the transducers with tractor-trailer angles. However, the correlation of the time measurements to tractor-trailer angle changes for each size and shape of tractor-trailer configuration. Consequently, a substantial amount of set up time is necessary to correlate tractor-trailer angles for transducer measurements for each configuration of tractor-trailer that is to use the Brown system. Also, the mirror must be calibrated manually to adjust to trailer position each time the Brown system is activated.
Thus, while the Brown system overcomes many of the drawbacks of the conventional art, this system is far from optimal. In particular, initial calibration can be very cumbersome. Also, configuring the look-up tables for each configuration of tractor and trailer is time consuming and expensive. Further, the look-up tables themselves do not always directly correlate to the time measurements indicative of the actual tractor-trailer angle so as to provide immediate accurate angle calculations. Instead, a great deal of averaging and manipulation of the time measurements, as well as estimates of the angle measurements from the look-up tables, are necessary for the operation of the Brown device. Consequently, real time measurement of the actual tractor to trailer angle with precise corresponding mirror tracking can be delayed unless the angle between the tractor and trailer is changing very slowly. Therefore, there is still a need for an accurate real-time automatic side view mirror tracking system that does not depend upon configuration of the tractor-trailer or the use of look-up tables.